The communities of investigators studying growth stimulatory or inhibitory substances have expanded to the point where treatment of all their essential concerns in a single meeting would be counterproductive. These meetings will convene joint sessions with topics important to both communities and treat topics of narrower focus concurrently. Growth factors regulate biological processes as diverse as embryogenesis, growth and development, wound healing, neoplasia, atherosclerosis, and cell differentiation, while negative regulators of cell proliferation play important roles in normal growth control and in the abnormal proliferation characteristic of cancer cells. Recently, many growth factor receptors and several potent inhibitors of both normal and transformed cell proliferation, including the type beta transforming growth factors, tumor necrosis factors, inhibins, and Mullerian inhibitory substance, have been purified and their genes cloned. The growth inhibitory properties of interferons have been explored and tumor suppressor genes identified. Much has been learned about responses that occur after growth factors interact with their receptors, although much remains to be learned concerning the nature of ligand-receptor interaction, the signals that are subsequently generated and the signal pathways leading to cell activation, the role of each of these factors in vivo, and the interrelationships among the different growth factors. In addition to secretion by many types of normal cells, neoplastically transformed cells secrete growth factors and their homologous. A further understanding of the synergistic activities of these factors or inhibition of their action by antagonists may help define roles in biology.